The Mouse Bioassay for Diarrhetic Shellfish Poisoning: A Gross Misuse of Laboratory Animals and of Scientific Methodology

The UK shellfish industry has recently been affected by the statutory closure of several cockle beds, following the detection of samples causing rapid and severe reactions in the regulatory approved test for diarrhetic shellfish poisoning (DSP) toxins, the mouse bioassay (MBA). It is contended that these so-called atypical results are due to procedural artefacts of the MBA; so far, several studies have failed to identify their cause. This paper critically assesses the development, regulatory use and methodological deficiencies of the MBA. It also discusses how testing for DSP toxins could and should have been improved and made more humane by applying the Three Rs concept of Reduction, Refinement and Replacement, and by the proper validation of the test method used. It is concluded that the MBA should not have been developed for the routine screening of shellfish samples, as it has a substantially severe endpoint and is not used as part of a tiered-testing strategy with non-animal methods. Moreover, during the UK monitoring programme for DSP toxins, the assay has been used without an optimised and universal protocol, and apparently without due regard to the principles of basic scientific methodology. In view of this, the atypical results obtained for cockle samples cannot be relied on as evidence of a human health hazard. It is recommended that the use of the MBA should be discontinued as soon as possible, in favour of other methods, especially those involving non-animal techniques. In the short-term, these methods should be based on analytical chemical detection systems and the essential availability of the relevant pure toxin standards. The lack of any known toxins in samples should be taken as evidence of lack of contamination. The suitability of the existing non-animal methods needs to be assessed as a matter of urgency. It is crucial that all new methods should be properly validated, and that their acceptability for their stated purposes should be endorsed by recognised criteria and validation centres, before being recommended to, or required by, regulatory agencies. In this way, the possibility that scientifically unsuitable methods will once again be used for monitoring for the contamination of shellfish with toxins can be avoided. This gross misuse of laboratory animals and ill-judged application of science should never be allowed to occur again.